Exactly half of your nuclear DNA is from your mom and half is from your dad. It’s the same for them with their parents. It goes on and on like that. There’s a really interesting technique called The Leeds Method that allows you to cluster your DNA matches and it basically groups your DNA matches into four main groups, one for each of your grandparents. So you can actually quite clearly, with a bit of family knowledge or research, see more or less how you’re related to a DNA match by comparing who your common matches are.

It’s hard to explain, but you can learn a lot about DNA matches who aren’t your immediate family.